A patient may need respiratory assistance as a result of disease and injuries of various kinds. The need can be direct, especially when the injury or illness afflicts the patient's respiratory system. The need can also be indirect, e.g. during anaesthesia and some intensive care. The respiratory assistance can encompass everything from facilitating spontaneous breathing to total control of breathing. Typically, a mechanical ventilator is employed to provide the breathing assistance.
One potential problem occurring in long-term controlled respiration is that the patient's own respiratory musculature becomes weakened. In many instances, the patient then loses the ability to breathe spontaneously after the true need for assisted respiration has been eliminated. Weaning the patient off the ventilator then takes longer. This causes a cost increase to the society in the form of longer treatment duration times and, more important, increases the discomfort and risk of secondary disease for the patient.
Amyotrophic Lateral Sclerosis (ALS, also known as Lou Gehrig's Disease or Motor Neuron Disease) is a progressive neurodegenerative disease of unknown cause. Approximately 1.4 individuals per 100,000 develop ALS annually and the peak incidence is between the ages of 55 and 75. The exact etiology of ALS is unknown although many potential causes have been proposed including exposure to neurotoxic agents, genetic or autoimmune disease, deficiencies of nerve growth factors, and viral infection. The typical clinical presentation is that of an individual with gradually progressive asymmetric weakness associated with hyperreflexia, muscle atrophy and fasciculations. Typically patients have difficulty with walking, balance, picking up objects, and eventually any limb muscle movement. The diagnosis of ALS is made on the basis of the history, a physical examination revealing upper and lower motor neuron signs, and electromyography demonstrating signs of disseminated active denervation and true reinnervation.
One effect of progressive neuromuscular weakness in patients with ALS is the effect on respiration. Although ALS has no direct effect on the lung, it has devastating effects on mechanical function of the respiratory system. ALS affects all of the major respiratory muscle groups: upper airway muscles, expiratory muscles, and inspiratory muscles. Therefore, all patients with ALS are at significant risk for respiratory complications. Progressive inspiratory muscle weakness in ALS inevitably leads to carbon dioxide retention, inability to clear secretions and hypercarbic respiratory failure, the major cause of death in ALS. At some point, ALS involves the respiratory muscles so severely that bulbar paresis is combined with severe expiratory and inspiratory muscle weakness and invasive ventilation becomes the only option for survival.